i965: Don't create a swrast context on ES2+.

i965: Don't create a swrast context on ES2+.

We already skip this for API_OPENGL_CORE; ES2+ is very similar.
The primary user of the swrast context is GL_SELECT and GL_FEEDBACK,
which have never existed in ES.

This saves approximately 18MB of memory in GLBenchmark 2.7 Egypt (ES2).
No regressions in es3conform on Ivybridge.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>